The increased turnover of the phospholipid phosphatidylinositol during stimulated secretion by endocrine and exocrine cells has been suspected to be required for increased flux of calcium ions across the cell membrane. Recent studies show that calcium ion-free conditions increase myoinositol uptake by pancreatic exocrine cells four-fold and result in almost all (96 percent) of the myionositol taken up to be incorporated into phosphatidylinositol. These results constitute the first unequivocal findings that some unknown aspects of phosphatidylinositol metabolism are directly related to calcium ion transport across the cell membrane. Studies are to be conducted (1) to determine the mechanisms responsible for the alteration of phosphatidylinositol metabolism under calcium ion-free phosphatidylinositol under calcium ion-free conditions are significantly different in islets isolated from control and homozygous, diabetic mice.